Method for preparing element diffusion-type composite substrate

ABSTRACT

A method for preparing element diffusion-type composite substrate and it belongs to the field of high-temperature coated superconducting substrate preparation. The rolled composite nickel-tungsten alloy substrate is heated and thermal insulated, meanwhile, both ends of the rolled substrate are electrified by low voltage and high current density pulse current. High-performance nickel-tungsten alloy composite substrate is obtained with the method in the present invention and sandwich-like composite substrate has low ferromagnetic performance and high strength by higher solution diffusing from inner layer to outer layer, which does not affect the formation of sharp cubic texture on the surface of substrate. On the one hand, electric pulse technology accelerate the interdiffusion effect of inter-layer elements, on the other hand, it promotes the recrystallization nucleation and reduces the recrystallization annealing temperature of the substrate, thus energy saving effect is achieved and the negative effects of annealing thermal erosion grooves among crystal boundary to subsequent coating are effectively reduced. Alloyed composite substrate prepared in this invention has the characteristics of high cubic texture content, low magnetic performance, high strength, and can be applied to large-scale industrial production.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims the priority benefit of Chinese application serial no. 201510030433.6, filed on Jan. 21, 2015, which the entirety the prior patent application is hereby incorporated by reference herein and made a part of this specification.

TECHNICAL FIELD

This invention relates to a method for preparing a cube textured nickel-tungsten alloy composite substrate used for high-temperature coated superconductor, and it belongs to the field of high-temperature coated superconducting substrate preparation.

BACKGROUND ART

Coated superconducting material is one of the high-temperature superconducting materials with broad application prospects and great potential commercial value. Among the textured metal substrate used for coated conductors, since the core of composite substrate is made of high-strength, non-ferromagnetic alloy material, the entire mechanical and magnetic properties of composite substrate with high cube textured surface are further improved, so composite substrate is one of the new metal alloy substrates with high performance and high potential application value. Element diffusion composite substrate is proven to be a high performance textured metal substrate used for coated conductor, which has capability to get sharp cube texture and has a good interface binding force between inner layer and outer layer.

Currently, Ni—W alloy substrate is one of the most widely studied substrate materials in scientific research. Compared to smelting method, powder metallurgy method for preparing a composite substrate is easier to achieve mutual diffusion of interlayers elements. In addition, it is required a much higher recrystallization temperature and has more pronounced diffusion effect than smelting does. Hot isostatic pressing technique is conducive to preparing large billets and achieve industrialization of composite substrate production. But exorbitant annealing temperature will deepen the depth and width of the thermal erosion groove, which is not conducive to further coating the transit layer on the surface of composite substrate. In view of this, powder metallurgy method is taken in the present invention for preparing element diffusion composite Ni—W alloy substrate. Annealing substrate in the furnace is electrified high-frequency and low-voltage large pulse current in the process of dynamic annealing, which thereby greatly enhances the interdiffusion of interlayer elements of composite substrate and reduces the recrystallization temperature of the substrate to some extent.

In the aspect of liquid metal solidification, pulse current leads to solidification temperature increase, solidification time shortening, temperature gradient decrease, solidification structure refinement and mechanical properties improvement; in the aspect of solid metal element diffusion, electric pulse technology can improve diffusion coefficient and reduce diffusion annealing temperature of the elements. Energy consumption decreases during high temperature annealing can reduce costs. Besides enhancing the interdiffusion effect of interlayer elements of composite substrate, the main effect of high-energy pulse is the interaction between electrons and dislocations can greatly enhance the process of recrystallization of the alloy, which just promotes recrystallization nucleation in the deformed tissue and has no significant effect on the mechanisms of nucleation in deformed band and the final texture of composite substrate.

In short, sandwich-like Ni—W alloy composite substrate prepared with powder metallurgic method is more conducive to mutual diffusion of interlayer elements, by which higher content W diffuses from the inner layer to the outer layer and the entire ferromagnetic performance of the composite base reduced. Electric pulse accelerated diffusion effect of the composite substrate elements, meanwhile improves the surface roughness of the composite substrate indirectly, so that the entire application performance of the composite substrate can be further improved.

The said method in the present invention can be applied to large-scale production of high-performance composite substrate by dynamic vertical annealing device.

CONTENTS OF THE INVENTION

This invention is to provide a method for preparing element diffusion type composite Ni—W alloy substrate in powder metallurgy method, characterized in following specific steps:

-   (1) The purity of greater than 99.9% of Ni powder and W powder are     proportioned according to the atomic percentage of W 8% and 12%,     respectively; after the proportioned raw materials are mixed evenly     by high-energy ball milling, the powder is hierarchically loaded     into the vacuum thin-wall wrap sequentially for hot isostatic     pressing, with the temperature of 1100˜1200° C., the pressure of 150     MPa and the time of 10˜30 min, respectively; preferentially, three     layer structured powder, with the volume ratio of 1:2:1, is     sequentially loaded into hot isostatic wrap material; wherein, Ni, W     mixed powder with higher W content is loaded into the middle layer. -   (2) After dealt with hot isostatic pressing for homogenization heat     treatment and hot rolling for cogging, the billet is cold rolled to     70˜100 nm thick composite tape; the total deformation is 99 to     99.3%; -   (3) Composite substrate is dealt with dynamic recrystallization     annealing heat treatment in a vertical heat treatment furnace     ventilating hydrogen argon protective atmosphere; moving rate of     5˜10 mm/min, total time of the composite substrate moving at     constant temperature area (1000˜1300 C) for 1 h˜2 h; at the same     time, pulse current is preferentially electrified to the annealing     composite substrate in the heat treatment furnace with the     parameters of electrode gap 900 mm, pulse frequency 150˜300 Hz,     current density 450˜650 A/mm² and DC voltage less than 5V; pulse     current directly acts on the surface of the composite substrate by     two metal guide rollers located on the top and bottom of heat     treatment furnace; metal guide wheels are made off oxygen-free     copper and connected to the positive and negative of pulse current     generator, respectively, annealing device schematic diagram is shown     in FIG. 1; composite substrate is eventually moved out of the heat     treatment furnace in coil take-up system, which gives rise to the     air-cooled.

The key to the present invention is to develop a technology for preparing special nickel-tungsten alloyed composite substrate used for coated conductor, further to achieve excellent performance alloyed substrate; compared to traditional single-layer nickel-tungsten alloy substrate, entire cube texture content, ferromagnetic properties and strength of the said substrate in this invention are improved; nickel tungsten alloy composite substrate prepared with the combination of powder metallurgy and electric pulse annealing technology is easier to achieve mutual diffusion of interlayer elements. The present invention can be applied to large-scale industrial production of composite substrate.

In the present invention, the rolled composite nickel-tungsten alloyed substrate is heated and thermal insulated, meanwhile, both ends of the rolled substrate are electrified by low voltage and high current density pulse current. High-performance nickel-tungsten alloy composite substrate is obtained with the method in the present invention and sandwich-like composite substrate has low ferromagnetic performance and high strength by higher solution diffusing from inner layer to outer layer, which does not affect the formation of sharp cube texture on the surface of substrate. On the one hand, electric pulse technology accelerate interdiffusion effect of inter-layer elements, on the other hand, it promotes the recrystallization nucleation and reduces the recrystallization annealing temperature of the substrate, thus energy saving effect is achieved and the negative effects of annealing thermal erosion grooves among crystal boundary to subsequent coating are effectively reduced. Alloyed composite substrate prepared in this invention has the characteristics of high cube texture content, low magnetic performance, high strength, and can be applied to large-scale industrial production.

DESCRIPTION OF FIGURES

FIG. 1 Annealing device schematic diagram;

FIG. 2 Element distribution curve along RD-ND section of Ni—W alloy composite substrate measured by EDS line scanning in exploit example 1;

FIG. 3 Element distribution curve along RD-ND section of Ni—W alloy composite substrate measured by EDS line scanning in exploit example 2;

FIG. 4 Element distribution curve along RD-ND section of Ni—W alloy composite substrate measured by EDS line scanning in exploit example 3;

FIG. 5 Element distribution curve along RD-ND section of Ni—W alloy composite substrate measured by EDS line scanning in exploit example 4;

FIG. 6 Distribution curve of element W content measured by XRF and cubic texture content measured by EBSD on the surface of Ni—W alloy composite substrate prepared in exploit example 1˜4;

The invention is further illustrated by description of figures and mode of carrying out the invention, which as below.

MODE OF CARRYING OUT THE INVENTION

This invention is further illustrated by the exploit examples, but is not limited by the following exploit examples.

Exploit Example 1

The purity of greater than 99.9% of Ni powder and W powder are proportioned according to the atomic percentage of W 8% and 12%, respectively; the proportioned raw materials are mixed evenly by high-energy ball milling and divided into three layers with the volume ratio of 1:2:1 and three-layer powder is hierarchically loaded into the vacuum thin-wall wrap sequentially for hot isostatic pressing, wherein, Ni, W mixed powder with higher W content is loaded into the middle layer, with the temperature of 1200° C., the pressure of 150 MPa and the time of 25 min, respectively; after dealt with hot isostatic pressing for homogenization heat treatment and hot rolling for cogging, the billet is cold rolled to 70˜100 nm thick composite tape, the total deformation is 99 to 99.3%; composite substrate is dealt with dynamic recrystallization annealing heat treatment in a vertical heat treatment furnace ventilating hydrogen argon protective atmosphere; moving rate of 10 mm/min, total time of the composite substrate moving at constant temperature area 1150° C. for 1 h; at the same time, pulse current is electrified to the annealing composite substrate in the heat treatment furnace with electrode gap of 900 mm, pulse frequency of 250 Hz, current density of 530 A/mm², DC voltage of 3V; composite substrate is eventually moved out of the heat treatment furnace in coil take-up system, which gives rise to the air-cooled; a length of the composite substrate samples completely goes through constant temperature area is cut and measured to get element distribution curve along the ND direction by EDS line scanning, as shown in FIG. 2.

Exploit Example 2

The purity of greater than 99.9% of Ni powder and W powder are proportioned according to the atomic percentage of W 8% and 12%, respectively; the proportioned raw materials are mixed evenly by high-energy ball milling and divided into three layers with the volume ratio of 1:2:1 and three-layer powder is hierarchically loaded into the vacuum thin-wall wrap sequentially for hot isostatic pressing, wherein, Ni, W mixed powder with higher W content is loaded into the middle layer, with the temperature of 1200° C., the pressure of 150 MPa and the time of 25 min, respectively; after dealt with hot isostatic pressing for homogenization heat treatment and hot rolling for cogging, the billet is cold rolled to 70˜100 nm thick composite tape, the total deformation is 99 to 99.3%; composite substrate is dealt with dynamic recrystallization annealing heat treatment in a vertical heat treatment furnace ventilating hydrogen argon protective atmosphere; moving rate of 5 mm/min, total time of the composite substrate moving at constant temperature area 1150° C. for 1 h; at the same time, pulse current is electrified to the annealing composite substrate in the heat treatment furnace with electrode gap of 900 mm, pulse frequency of 250 Hz, current density of 530 A/mm², DC voltage of 3V; composite substrate is eventually moved out of the heat treatment furnace coil take-up system, which gives rise to the air-cooled; a length of the composite substrate samples completely goes through constant temperature area is cut and measured to get element distribution curve along the ND direction by EDS line scanning, as shown in FIG. 3.

Exploit Example 3

The purity of greater than 99.9% of Ni powder and W powder are proportioned according to the atomic percentage of W 8% and 12%, respectively; the proportioned raw materials are mixed evenly by high-energy ball milling and divided into three layers with the volume ratio of 1:2:1 and three-layer powder is hierarchically loaded into the vacuum thin-wall wrap sequentially for hot isostatic pressing, wherein, Ni, W mixed powder with higher W content is loaded into the middle layer, with the temperature of 1200° C., the pressure of 150 MPa and the time of 25 min, respectively; after dealt with hot isostatic pressing for homogenization heat treatment and hot rolling for cogging, the billet is cold rolled to 70˜100 nm thick composite tape, the total deformation is 99 to 99.3%; composite substrate is dealt with dynamic recrystallization annealing heat treatment in a vertical heat treatment furnace ventilating hydrogen argon protective atmosphere; moving rate of 10 mm/min, total time of the composite substrate moving at constant temperature area 1250° C. for 1 h; at the same time, pulse current is electrified to the annealing composite substrate in the heat treatment furnace with electrode gap of 900 mm, pulse frequency of 280 Hz, current density of 610 A/mm², DC voltage of 3V; composite substrate is eventually moved out of the heat treatment furnace in coil take-up system, which gives rise to the air-cooled; a length of the composite substrate samples completely goes through constant temperature area is cut and measured to get element distribution curve along the ND direction by EDS line scanning, as shown in FIG. 4.

Exploit Example 4

The purity of greater than 99.9% of Ni powder and W powder are proportioned according to the atomic percentage of W 8% and 12%, respectively; the proportioned raw materials are mixed evenly by high-energy ball milling and divided into three layers with the volume ratio of 1:2:1 and three-layer powder is hierarchically loaded into the vacuum thin-wall wrap sequentially for hot isostatic pressing, wherein, Ni, W mixed powder with higher W content is loaded in the middle layer, with the temperature of 1200° C., the pressure of 150 MPa and the time of 25 min, respectively; after dealt with hot isostatic pressing for homogenization heat treatment and hot rolling for cogging, the billet is cold rolled to 70˜100 nm thick composite tape, the total deformation is 99 to 99.3%; composite substrate is dealt with dynamic recrystallization annealing heat treatment in a vertical heat treatment furnace ventilating hydrogen argon protective atmosphere; moving rate of 5 mm/min, total time of the composite substrate moving at constant temperature area 1250° C. for 2 h; at the same time, pulse current is electrified to the annealing composite substrate in the heat treatment furnace with electrode gap of 900 mm, pulse frequency of 280 Hz, current density of 610 A/mm², DC voltage of 3V; composite substrate is eventually moved out of the heat treatment furnace in coil take-up system, which leads to the air-cooled; a length of the composite substrate samples completely goes through constant temperature area is cut and measured to get element distribution curve along the ND direction by EDS line scanning, as shown in FIG. 5. 

What is claims is:
 1. A method for preparing element diffusion-type composite Ni—W alloy substrate, characterized in comprising the steps of: (1) The purity of greater than 99.9% of Ni powder and W powder is proportioned according to the atomic percentage of W 8% and W 12%, respectively; after the proportioned raw materials are mixed evenly by high-energy ball milling, the powder is hierarchically loaded into the vacuum thin-wall wrap sequentially for hot isostatic pressing, with the temperature of 1100˜1200° C., the pressure of 150 MPa and the time of 10˜30 min, respectively; (2) After dealt with hot isostatic pressing for homogenization heat treatment and hot rolling for cogging, the billet is cold rolled to 70˜100 nm thick composite strip; the total deformation of billet is 99 to 99.3%; (3) Composite substrate is dealt with dynamic recrystallization annealing heat treatment in a vertical heat treatment furnace ventilating hydrogen argon protective atmosphere; moving rate of 5˜10 mm/min, total time of the composite substrate moving at constant temperature area (1000˜1300° C.) of 1 h˜2 h; at the same time, pulse current is electrified to the annealing composite substrate in the heat treatment furnace hearth; complex substrate is eventually moved out of the heat treatment furnace in coil take-up system, which gives rise to the air-cooled.
 2. The method for preparing element diffusion-type composite Ni—W alloy substrate according to claiml, characterized in that: three-layer structured powder, with the volume ratio of 1:2:1, is sequentially loaded into hot isostatic wrap material; wherein, Ni, W mixed powder with higher W content is loaded into the middle layer.
 3. The method for preparing element diffusion-type composite Ni—W alloy substrate according to claim 1, characterized in that: the parameters of electrical pulse used include the electrode gap of 900 mm, the pulse frequency of 150˜300 Hz, the current density of 450˜650 A/mm², the DC voltage of less than 5V.
 4. The method for preparing element diffusion-type composite Ni—W alloy substrate according to claim 1, characterized in that: the said pulse current directly acts on the surface of the composite substrate by two metal guide rollers located on the top and bottom of heat treatment furnace hearth; metal guide wheels are made of oxygen-free copper and connected to the positive and negative of pulse current generator, respectively.
 5. The method for preparing element diffusion-type composite Ni—W alloy substrate according to claim 2, characterized in that: the said pulse current directly acts on the surface of the composite substrate by two metal guide rollers located on the top and bottom of heat treatment furnace hearth; metal guide wheels are made of oxygen-free copper and connected to the positive and negative of pulse current generator, respectively.
 6. The method for preparing element diffusion-type composite Ni—W alloy substrate according to claim 3, characterized in that: the said pulse current directly acts on the surface of the composite substrate by two metal guide rollers located on the top and bottom of heat treatment furnace hearth; metal guide wheels are made of oxygen-free copper and connected to the positive and negative of pulse current generator, respectively. 